1. Field of the Invention
The present invention relates to the measurement of the deflection of underlying surfaces. More particularly, the present invention relates to systems and processes for measuring the angle of deflection of the rail or pavement when subjected to the load of a wheel. Additionally, the present invention relates to laser-based systems for measuring such deflections.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The loadbearing capability for pavements and rails may deteriorate, over time, due to a number of factors, including changes in the elastic moduli of subpavement layers of earth. In order to determine pavement conditions for highways, the loadbearing capability of the pavement can be periodically tested. In order to measure the loadbearing capability of the pavement, it is desirable to utilize technologies that are nondestructive so that the integrity of the pavement layers is maintained. Further, it is important that the measurement should be made rapidly, through an automated system, so as to minimize time and reduce costs.
Different methods have been developed for the non-destructive testing of pavements, with one utilizing a falling weight dropped on the pavement from a stationary platform. Sensors than measure the deflection of the pavement at intervals out from the falling weight. Systems utilizing this method of time commonly referred to as falling weight deflectometers.
Other systems utilize a fast-moving, heavy wheel load that rolls along the pavement, with sensors being arranged at intervals out from the wheel to measure deflections. Systems utilizing this approach are commonly referred to as rolling wheel deflectometers. In essence, a load is placed on a wheel that rolls across the pavement and the depth of a deflection basin created by the loaded wheel is measured using precision laser sensors mounted on a horizontal member that tracks with the wheel. Such deflection measurements provide insight into the loadbearing capability of the pavement.
The current technology is very limited in the measurement of pavement deflections. Measurements of deflection can vary between 20 and 50% between falling weight deflectometers, and rolling wheel deflectometers depending on pavement temperature, texture, stiffness, composition, and deflection magnitude. Rolling wheel deflectcometers provide measurements that are combination of deflection, load and texture. The measured deflection is the sum of the actual pavement deflection and the vertical vibration of the layers mounted onto the vehicle.
An area of concern with rolling wheel deflectometers is the compromise between precision and the loss of details associated with spatial averaging. This is of particular concern with measurements that are being taken at high speeds. In general, an averaging of approximately ten meters or more is required in order to reduce the large random errors in the individual measurements caused by bouncing, texture and vibrations of the vehicle.
In addition to the major detrimental effects of vibration and texture, two additional forces require evaluation as the velocity of data acquisition increases. In particular, there can be sideways sway or “rock 'n roll” as the vehicle travels. This lateral shifting exerts a time-varying load on the wheels from side-to-side. If this vehicle is also measuring deflection, either on rails or pavement, then the measured deflection needs to be corrected for the time-varying load. Current practice ignores this effect and assumes the load is constant.
Additionally, at current load data acquisition speeds, the deflection basin is assumed to be symmetrical about the load wheel and back calculations are used to obtain pavement (or railbed) parameters based on a “static load” model. As data acquisition speeds increase, the static model becomes less viable and the deflection basin formed by the moving load will not be symmetrical.
The texture problem fundamentally exists because the diameter of the laser beams is small compared to the irregularities in the pavement surface. This problem is exacerbated by the deliberate efforts to roughen the pavement surface in order to increase water drainage and traction between tires and pavement surface. Further exacerbation is caused by deterioration of the pavement through patching and cracking.
The effective vertical vibration on the total deflection measurement is more difficult to isolate and evaluate. The railroad industry has an analogous problem to the pavement management fraternity where track modulus is analogous to pavement deflection. Rail and pavement deflection measures the competence of the structure supporting the rolling loads, either trains or vehicles. The major difference in noise problems (i.e. vertical vibration and texture) based by rail and pavement engineers is that the smooth rail track surface does not have the texture problem built into pavement surfaces.
As the pavement surface quality deteriorates, deflection measurement quality also deteriorates from a combination of surface reflectance quality, increased roughness and increased vertical vibration. One rolling wheel deflectometer problem is the vertical vibration of the railcar or trailer holding the lasers. Rough pavement primarily affects the pavement deflectometer. Hence, the noise level measured by the railcar deflectometer is a good measure of the vertical vibration component in the rolling wheel deflectometer measurements. An additional problem is the combination of deflection and surface texture. As pavement ages and the surface deteriorates, laser reflectivity rapidly degrades, making accurate measurements problematic. The vertical vibration component of the measurement noise also increases rapidly with deteriorating pavement surface quality.
In the past, various patents have issued with respect to the measurement of pavement deflection.
For example, U.S. Pat. No. 3,383,913, issued a May 21, 1968 to G. Swift, is an early patent disclosing measurement of pavement deflection. In this patent, a moving vehicle applies a load to the underlying surface. A first carriage is moved by the vehicle having a structural displacement sensing device mounted thereon which is adapted to sense structure displacement near the point of application of the load. A second carriage is moved by the vehicle simultaneously with the first carriage. The second carriage also has a displacement sensing device adapted to sense structural displacement sufficiently removed from the point of application of the load to the structure so as to be unaffected by the load. Suitable electrical signals are transmitted so as to be indicative of the deflection.
U.S. Pat. No. 3,427,877, issued on Feb. 18, 1969 to Swift et al., discloses a dynamic deflection determination device. This device includes a two-wheeled trailer and a force applying assembly mounted to the trailer. A motion sensing device detects deflections of the structure resulting from the application of a cyclic force. The motion sensing device is mechanically coupled to the structure. Electrical signals are transmitted indicative of the movement detected by the motion sensing device.
U.S. Pat. No. 4,571,695, issued on Feb. 18, 1986 to Elton et al., discloses a non-contact road profilometer and deflection meter. This apparatus includes a rigid frame attached to a vehicle, first, second and third profile detecting means, and a controller for simultaneously instructing the profile detecting means to activate to cause the distance to be simultaneously measured between the frame and the underlying road surface at three laterally spaced-apart locations. This provides a set of distance data.
U.S. Pat. No. 4,788,859, issued on Dec. 6, 1988 to A. S. Khattak, shows a method for direct measurement of the vertical displacement of a point on a surface of the pavement upon application of a load thereto. The method measures the vertical displacement through the use of optical equipment. The displacement is equivalent to the vertical movement of an optical focusing element between the position of the element when a point on the surface of the pavement is in focus with and without the application of the load. The point linear displacement measurement can be applied to the calculation of a volumetric displacement.
U.S. Pat. No. 5,046,366, issued on Sep. 10, 1991 to Basson et al., shows a method for measuring deflection or deformation in pavement structures. The system includes at least one apparatus including an electric coils sensitive to relative movement between them at a relatively anchored body of ferromagnetic material. A pair of longitudinally-spaced relatively movable discs and a body of resilient transversely extendable material is positioned between the discs. A nut serves to urge the discs toward one another so as to cause the body transversely to expand to secure the apparatus at a predetermined depth against a wall in a test hole.
U.S. Pat. No. 6,119,353, issued on Sep. 19, 2000 to L. Gronkov, discloses a method and apparatus for non-contact measuring of the deflection of roads or rails. This equipment includes a self-propelled vehicle with a load which influences at least one wheel. The speed of the wheel is measured in the direction of travel. A laser device includes at least one electromagnetic beam directed toward the roadway in the vicinity of the vehicle. A Doppler frequency change in the reflection is detected. An electronic circuit continuously registers the results of the measurements and, as such, the deflection at a normal traveling speed.
U.S. Pat. No. 5,753,808, issued on May 19, 1998 R. F. Johnson, teaches a self-compensating rolling weight deflectometer for the measurement of a pavement under load. The deflectometer incorporates an alignment laser beam emitter that measures vertical displacement of each of the plurality of distance sensors is mounted on a horizontal sensor bearer member that bends or vibrates as it is transported over a pavement for deflection measurement. The measured vertical displacements, due to member bending, allows the deflectometer to compensate for errors introduced by member bending and thereby provide a more accurate measurement of pavement deflection.
U.S. Pat. No. 8,596,113, issued on Dec. 3, 2013 P. Ullidtz, provides an improved non-destructive testing of pavements using rolling wheel deflectometers having more than four sensors. The additional sensors accurately detect pavement deflections under load by compensating for the influence of the load deflection basin. The sensors are positioned beyond the wheel load. The sensors are spaced with equal distances from the rolling weight and can have a distance between adjacent sensors that is greater than the equivalent thickness of the pavement being measured.
U.S. Patent Publication No. 2012/0010828, published on Jan. 12, 2012 P. Ullidtz, describes a rolling weight deflectometer having sensors to measure pavement deflection. The sensors provide test data to determine the subgrade modulus and equivalent thickness of the pavements. This information is then utilized to determine more than deflection and is utilized to determine critical strain parameters so as to predict bearing capacity, rutting and roughness characteristics of pavements.
It is an object of the present invention to provide a system and process for measuring deflection which avoids the problems associated with vertical vibration of the sensors.
It is another object of the present invention to provide a system and process for measuring deflection that overcomes the effect of texture and reflectance quality on laser spot reflectivity.
It is another object of the present invention to provide a system and process for measuring deflection which avoids corruption of pavement deflection measurement.
It is another object of the present invention to provide a system and process for measuring deflection which dynamically measures load.
It is another object of the present invention to provide a system and process for measuring deflection that eliminates vertical vibration noise components.
It is still a further object of the present invention to provide a system and process for the measuring of deflection which measures the angle of deflection in order to calculate the amount of deflection.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.